linux-kernel - Re: [RFC/PATCH] extcon: otg_gpio: add driver for USB OTG port controlled by GPIO(s)

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Date:	Wed, 24 Dec 2014 11:08:52 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	David Cohen <david.a.cohen@...ux.intel.com>
CC:	<myungjoo.ham@...sung.com>, <cw00.choi@...sung.com>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	<baolu.lu@...ux.intel.com>
Subject: Re: [RFC/PATCH] extcon: otg_gpio: add driver for USB OTG port
 controlled by GPIO(s)

On Tue, Dec 23, 2014 at 11:40:23AM -0800, David Cohen wrote:
> Hi Peter,
> 
> Thanks for the review.
> 
> On Tue, Dec 23, 2014 at 09:25:18AM +0800, Peter Chen wrote:
> > On Mon, Dec 22, 2014 at 02:43:37PM -0800, David Cohen wrote:
> > > Some platforms have an USB OTG port fully (or partially) controlled by
> > > GPIOs:
> > > 
> > > (1) USB ID is connected directly to GPIO
> > > 
> > > Optionally:
> > > (2) VBUS is enabled by a GPIO (when ID is grounded)
> > > (3) Platform has 2 USB controllers connected to same port: one for
> > >     device and one for host role. D+/- are switched between phys
> > >     by GPIO.
> > 
> > Would you explain how it works? Choosing controller runtime?
> 
> Both controllers are (indirectly) connected to the same micro B port.
> The D+/- goes from the port to a switch operated by a GPIO. From the
> switch, D+/- may go to Host controller's phy or Device controller's phy.
> Depends on the GPIO level.
> 

Get it, why the design like that? If your controller supports both
roles, the software can do role switch by ID pin (through gpio in your
case).

> > 
> > > 
> > > As per initial version, this driver has the duty to control whether
> > > USB-Host cable is plugged in or not:
> > 
> > You mean Micro-AB cable, right?
> 
> > > +
> > > +	vup->gpio_usb_mux = devm_gpiod_get_index(dev, "usb mux",
> > > +						 VUPORT_GPIO_USB_MUX);
> > > +	if (IS_ERR(vup->gpio_usb_mux))
> > > +		dev_info(dev, "cannot request USB USB MUX, skipping it.\n");
> > 
> > Using dev_err
> 
> That's not really an error, although the IS_ERR() suggests otherwise.
> The driver works well if a board doesn't need this mux (I'll add a
> comment to state that clear). IMHO either keep dev_info or use dev_dgb
> instead?
> 

If that, dev_dbg may be suitable.


-- 

Best Regards,
Peter Chen
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